Process of treating monocyclic terpene hydrocarbons



Patented Aug. 13, 1940 PATENT OFFICE 2,211,432 V Paocnss or rename mouocgcuo Tsa- 'PENE HYDBOCARBO Robert O. Palmer and Garlisle H. Blbbilensacola, Fla minors to Newport Industries, Inc., Pensacola, Fla., a corporation of Delaware No Drawing. Application August 19, 1938, Serial No. 225,124

4 13 Claims. (Cl. 260-866) This invention relates to a process of treating monocyciic terpene hydrocarbons, and more particularly to a process of preparing p-cymene from a monocyclic terpene hydrocarbon or a mixture thereof by liquid phase catalysis' It hasheretofore been proposed to produce 1)- cymene by dehydrogenation of terpene hydrocarbons in vapor phase in the presence of a catalyst. It has also been produce cymene by treatment of terpenes,'either in liquid or vapor phase, with heat in the presence of fullers earth. This latter process, however, does not lead to therecovery of cymene even in a state of technical purity.

According to our present process, monocyciic terpene hydrocarbons may be converted substantially completely into a relatively pure mixture of p-cymene and p-menthane by simply refluxing the terpene hydrocarbons in the presence of a monocyciic terpene hydrocarbons by refluxing catalyst capable of bringing about a simultaneous dehydrogenation and hydrogenation of the tere penes. We have further found that neither c019- per nor nickel alone, as'catalysts, will give satisfactory yields, but that by the use of a mixture of both of these metals, in active form, very satisfactory yields can readily be .obtained. The

. separation of the reaction product, resulting from the liquid phase catalytic hydrogenation and dehydrogenation of the monocyciic terpene'hydrm carbons, can be effected, in accordance with our by a fractional distillation to obtain p-menthane and relatively pure psuch hydrocarbons at temperatures below 200' C. in the presence of a mixed catalyst containing copper and nickel.

Other and further invention will become ing description and appended claims.

The monocyciic terpene hydrocarbons that m suitable-for use as starting materials for the production of p-cymene include-all of these hydro-- carbons having the empirical formula 6101111, and

mixtures thereof which belong-to the para-menthane. 'series, particularly commercial mixtures h own in the trade as dipentene," dytin,"

proposed in the Humphrey Patent No. 1,746,532, dated February 11, 1930.1.0

important objects of mu apparent from the followsolvenol," and the like, which are composed of dipentene, dand l-limonene, terpinene, terpinolene, and similar isomeric compounds.

In the case of such commercial mixtures, we have found that a change readily takes place on storage, due to the fonnation of small amounts of materials, possibly peroxides, which greatly interfere with the liquid phase hydrogenation-dehydrogenation reaction employed in our process, or even prevent such reaction entirely, but we have also found that a simple distillation of the terpene hydrocarbon oil over a small quantity of caustic alkali, such as 1% by weight of sodium hydroxide, or its equivalent, will restore the ofl to a reactive condition. The caustic alkali may be added to the terpene hydrocarbon oils either in a dry state or as a water solution. Alternatively, the reactivity of an old 011 may be restored by redistillation of such old oil inthe absence of any alkali, but leaving a residue of undetermined amount in the still.

. Our process involves the simultaneous hydro genation and dehydrogenation of the monocyciic ,terpene :hydrocarbons to p-menthane and pcymene. The reaction will theoretically be a complete dehydrogenation of a major portion of the terpene to p-cymene with a complete hydrogenation oi the minor portion to p-menthane, but in practice there may be present in the final crude mixture some menthene, depending upon the severity of the reaction. Therefore, practicallyall of the monocyciic terpene hydrocarbons boiling between 170 to 190 C. are suitable for conversion in accordance with the process of our invention.

Briefly, our process consists in refluxing the monocyciic terpene hydrocarbons with a mixed catalyst containing nickel and copper, in an active form, at atmospheric pressure until the reactions are complete and thenfractionally distilling, preferably under reduced pressure, the reaction products so formed, taking 'oil a heads cut of menthene, an intermediate cut for redistillation, and a ilnal cut of p-cymene.

.. The reaction in the presence "of the mixed catalyst liberates considerable heat which must be controlled either-by the amount of catalyst used or by feeding the hydrocarbons into a small quantity of reacted oil and suspended catalyst. Dipentene, for example, is decidedly unstable at its boiling p i t in the presence of the finely divided catalysla'whereas a mixture of cymene and menthane isinert under .the same conditions. on account of the considerable diilerence in heat content of the two mixtures and the vigorous nature of the reaction at the start, due to the relative purtiy of the initial reacting materials, the boiling of the mixture would be too violent to be handled unless the catalyst were used in a very small amount. However, enough catalyst must be employed so that when the mixture becomes increasingly diluted with reaction products the reaction can still be completed within a reasonable time.

The catalyst that we prefer to employ is a finely divided mixture of metallic copper and nickel with probably some oxides of these metals. This catalyst is added originally as the mixed formates of the metals. The formatesare thermally decomposed, during the heating of the oil, to the active catalytic form, and during such decomposition give off. a small amount of gas and water, which must be removed. The catalyst can be used several times, but the reaction is greatly prolonged after, say, the third, or fourth reuse. For practical operation, half of the catalyst is removed at the end of each batch and fresh catalyst added to replace it for the next batch.

The first batch of monocyclic terpene hydrocarbons, to be treated in accordance with the process of our invention, is preferably handled differently from the succeeding batches. In the first batch, the 'oil is brought to reflux and the mixture of copper and nickel formate is gradually fed in as the reaction proceeds. In the succeeding batches some reacted oil is left in the vessel so that it may be refluxed to suspend the used catalyst, the fresh oil then being fed into this under controlled boiling conditions. About 50% of the used catalyst is removed each time and an equivalent amount of fresh catalyst added so as to maintain a constant catalyst activity. The catalyst settles out very mixure, thereby making it possible to bulk of the oil from the catalyst.

The following example will serve to illustrate a preferred embodiment of our invention, it being "understood, however, that the conditions specified in the example-are illustrative merely and not intended to limit the scope of this invention.

While a positive refluxing of the reaction mixture automatically controls the temperature at a decant the desired point and facilitates the operation of the process, it is not essential to the invention to reflux the mixture. The reaction proceeds before the reflux temperature is reached, and as the temperature is advanced the velocity of the reaction is increased. Practical results can be obtained by heating the mixture, preferably with to a temperature lower than the reflux temperature at atmospheric pressure, such temperature being only high enough to convert the formates to an active form of catalyst and to enable the reaction to be carried to completion in a' practical length of time. If more catalyst is used, the temperature may be lower, and vice versa.

Refiuxing could also be obtained by carrying out Y the reaction at below atmospheric pressure with a condenser between the reaction vessel and the vacuum pump or ejector, so that the non-condensable gases are carried away. The process,

therefore, is broadly the application-of heat to the reaction mixturein the liquid' phase.

Example 1000 gals. of freshly distilled "dipentene or dytin, or other mixture of monocyclic terpene hydrocarbons, are charged into a kettle and brought to the boiling point under a reflux condenser. 140 lbs. of the copper-nickel formate the kettle and the kettle pressure as well from the reactedcataly'st are gradually fed in over a period of about 1% to 2 hours, care being taken that the oil does not boil too violently by cutting down the application of heat during this period. The mixture is then refluxed, the temperature advancing from 174 to 178 0., for 8 hours or more. tapping off any water that may be formed and allowing any excess hydrogen that is liberated to escape. Thereafter, the reaction mass is allowed to cool somewhat and pumped to a cooling tank,

leaving about 100 gals. in the kettle. About 50% of the catalyst is preferably removed'from the kettle, and if this amount does not go to the cooling tank during the withdrawal of the oil, the residual oil in the kettle is agitated and that quantity of oil removed that is necessary to leave 50% of the catalyst in the kettle.

All succeeding batches are handled differently from the first, as follows: 70 lbs. of fresh catalyst are added to the residual oil and catalyst in heated to a refluxing temperature. 1000 gals. of oil are then run in over a period of 2 hours, using the same precautions as in the first run when adding the catalyst. After all. the oil is in, the mixture is refluxed for 8 hours more, cooled, dumped and 50% of the catalyst removed as before. Succeeding batches are handled in the same manner as the second run, just described.

The. crude reaction mass consists of somewhat p-menthane. Separation of p-cymene is accomplished by fractional distillation under as low will permit efllcient recovery of the distillates. An absolute pressure of 15 mm. of mercury has been found satisfactory. At this reduced pressure, p-menthane boils approximately at 58 C. and p-cymene at 66 C. In order to produce the first fraction, which is desirably menthane containing very little cymene, severe fractiona'ting conditions are necessary. Likewise, the same conditionsare required in order that the intermediate, or next cut, will be fairly small. The p-cymene may be distilled straight over after the intermediate cut, producing a grade which will not be quite so good as when a rough fractionation is used, because of the presence of a very small amount of high boilers.

As illustrative of the results to be obtained on a small scale fractional distillation, the following description is given: 1000 cc. of the crude reaction product, as obtained above, was put in a still consisting of a 3-liter flask provided with a refluxing column 1% inches in diameter by 40 inches in length, filled with small porcelain saddles. Fractionation was made with about a 10- to-l reflux ratio, the distillate rate being 60 cc. per hour during the menthane and intermediate cuts. The cymene was distilled out with a 1-to-1 reflux ratio at the rate of 500 cc. per hour. The fol lowing table shows the results.

'lem Vol. cc. Mm

o Sp. gr. R. L

gi 313 vacuum 159/4 emuks 56 100 12. 5 8084 1. 4441 59 100 r 12- 5 8115 1. 4460 Menthanocut. 6O 50 12. 5 8143 1. 4482 v 63 50 1?. 5 8437 1. 4722 Intermediates cut.

63.5..." 50 12.5 .8581 1.4851 65 4s l2. 5 secs 1. 4891 65.5"-.. 255 12.5 r .8605 1. 4908 cymene cut. 65.5-.. 230 12.5 .8606 1.4913

The intermediates out were added to the succeeding batch and redistilled therewith. The

boiling range of the p-cymene thus produced, be-

tween 5% and 95%, was from 177.0 to 177.8 C.

The reaction isnot limited to .the amount of catalyst shown in the example, wherein the weight of the catalyst is approximately 2% by weight of the oil, since as little as 1% is effective for freshly distilled oil, although the time of reaction is somewhat prolonged. Larger amounts T0 of catalyst only speed up the operation, and if too much catalyst is used the reaction may become too violent to be controlled.

A satisfactory ratio of copper to nickel'is 3 parts of copper to 1 part of nickel by weight, as

shown in the preceding example. While this ratio is preferred for economical operation, any ratio which will effectively perform the-reaction is included, such as equal quantities of each metal.

0 While the mixed commercial formates of copper and nickel are moderately satisfactory for use in our process, we have found that the best results are secured with a special catalyst prepared by the action of formic acid on the mixed 5 carbonates of the metal. This insures an intimate mixture of the oxides and the metals when the catalyst is in its final reduced active form.

The preferred mixed catalyst is prepared as follows: '75 lbs. of copper carbonate and lbs.

of nickel carbonate are put in a double-bottom pan and 100 lbs. of water added and stirred'in. Then 85 lbs. of 90% formic acid are added grad ually or in small amounts at a time. and stirred. When the liberation of carbon dioxide subsides,

another portion of the acid is added, and this continued until all the acid is in. This will produce a soupy mixture. (ionsiderable heat is evolved during the reaction. Steam is then turned on the false bottom and the formates evaporated down to dryness. During this evaporation, the mixture must be stirred, particularly during its.solidification. In so doing, the formates are reduced to a powdered form. In the absence of agitation, the mass will cake and then have to be broken up. The least amount of steam pressure in the jacket should beused in order to prevent temperatures above 100 C. in the formates. There will be some tendency, in spite of this, for the catalyst to blacken on the surface $0 of the pan, but this does no harm if in reasonable amounts. A good grade of commercial 90% formic acid and a commercial grade of nickel and copper carbonates can be used satisfactorily.

We are aware that numerous details of the i5 process may be varied through a wide range without departing from the principles of this invention, and we thereforedo not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

0 We claim as our invention:

1. In the process of treating monocyclic terpene hydrocarbons, the step which comprises heating such hydrocarbons to reaction temperatures in the liquid phase in the presence of a catalyst 5 containing effective amounts of both copper and nickel in an active form to effect a substantially complete conversion of said hydrocarbons into p-cymene and p-menthane.

2. The process of treating monocyclic terpene p hydrocarbons which comprises heating such sion of said hydyrocarbons into p-cymene and p-menthane and recovering said p-cymene.

3. The process of producing lJ-cymene frommonocyclic hydrocarbons of the empirical formula CiOHiB which comprises heating such hydro- 5 carbons under reflux conditions in the presence of a mixed catalyst containing copper and nickel in effective quantities and in an active form until said hydrocarbons have been largely converted into p-cymene and p-menthtane and recover- 1 ing said p-cymene.

4.".lhe process of producing p-cymene from monocyclic hydrocarbons of the empirical formula Cl0Hl6 which comprises heating such hydrocarbons in liquid phase under reaction conditions 35 in the presence of a mixed catalyst containing eifective quantities of both copper and nickel in an active form until said hydrocarbons have been largely converted into p-cymene and p-menthane and separating said p-cymene from the 20 resulting reaction mass by fractional distillation.

5. The process of preparing p-cymene from monocyclic terpene hydrocarbons of the empirical formula cioHis which comprises heating a batch of a freshly distilled monocyclic terpene 25 hydrocarbon to reaction temperatures in the presence of a mixture of effective quantities of copper and nickel in catalytically active form suspended in the hydrocarbon liquid phase, continuing heating until the reaction is substantially complete, cooling, separating part of said cata lytic mixture for reuse and recovering p-cymene from the resulting reaction mass.

6. The process of preparing p-cymene from monocyclic terpene hydrocarbons of the empiri- 35 cal formula CmHm, which comprises heating a batch of a freshly distilled monocyclic terpene hydrocarbon to reflux temperatures in the presence of a mixture of efiective quantities of copper and nickel in catalytically active form suspended in 40 the hydrocarbon liquid phase, continuing refluxing until the reaction is substantially complete, cooling, separating part of said catalytic mixture for reuse and fractionally distilling under vacuum to recover p-cymene from the resulting reaction 45 mass.

. 7. The process of preparing p-cymene from monocyclic terpene hydrocarbons of the empirical formula CmHm, which comprises heating a batch of a freshly distilled monocyclic terpene hydrocarbon to reaction temperatures in the presence of about 1 to 2% by weight of a mixture of 3 parts by weight of copper and 1 part by weight of nickel in catalytically active form suspended in the hydrocarbon liquid phase, continuing heating until the reaction is substantially complete, cooling, separating part of said catalytic mixture for reuse and recovering p-cymene from the resulting reaction mass.

8. The process of preparing p-cymene from monocyclic terpene hydrocarbons of the empirical formula CinHm, which comprises heating a batch of a freshly distilled monocyclic terpene hydrocarbon to reflux temperatures in the presence of about 2% by weight of a mixture of 3 05 parts by weight of copper and 1 part by weight of nickel in catalytically active form suspended in the hydrocarbon liquid phase, continuing refiux= ing until the reaction is substantially complete,

cooling, separating part of said catalytic mixture to for reuse and fractionally distifiing under vacuum to recover p-cymene from the resulting reaction mass.

9. The process of preparing p=cymene from monocyclic terpene hydrocarbons oi the empirb 15 cal formula CmHie, which comprises heating a monocyclic terpene hydrocarbon to a reflux temperature, adding gradually a copper-nickel catalyst containing effective quantities of both metals to the hydrocarbon liquid phase, continuing the refluxing of the resultingmass imtil the reaction is substantially complete, trapping oiI any water formed, cooling said mass and fractionally distilling said mass under partial vacuum to recover p-cymene therefrom.

10. The method of preparing p-cymene, which comprises heating under reflux conditions a monocyclic terpene hydrocarbon with a mixture of catalytically active copper and nickel in effective 'quantities in suspension in the liquid phase of said hydrocarbon, continuing refluxing until a substantially complete conversion of said hydrocarbon into p-cymene and p-menthane has been effected and iractionally distilling the resulting reaction mass under reduced pressure to separate p-cymene therefrom.

11. The method of preparing p-cymene, which comprises heating under reflux conditions a monocyclic terpene hydrocarbon with at least 1% by weight a mixture containing an efiective proportion of catalytically active copper and nickel in suspension in the liquid phase or said hydrocarbon, continuing refluxing until a substantially complete conversion of said hydrocarbon into pcymeneand p-menthane has been efiected and fractionally distilling the resulting reaction mass under-greatly reduced pressure to separate p-cymene therefrom.

12. The method of preparing pcymene, which comprises heating a ireshly distilled monocyclic terpene hydrocarbon to reflux, gradually adding to the liquid phase at least 1% by weight of a copper-nickel formate catalyst, said catalyst containing effective proportions of copper and nickel, refluxing the resulting mixture until the reaction is substantially complete, removing a large proportion of said reaction mixture including about-% of said catalyst, adding fresh catalyst to the remaining reaction mixture and slowly adding thereto additional fresh terpene hydrocarbon, refiuxing and removing a large proportion of the further reaction mixture as before, and fractionally distilling the removed reaction mixtures under reduced pressure to recover p-cymene therefrom.

13. The process of preparing p-cymene from a mixture of monocyclic terpene hydrocarbons all of the empirical formula CmHm, which comprises heating such mixture in liquid phase to reaction temperatures in contact with catalytically effective amounts of both active copper and nickel to bring about a simultaneous dehydrogenation and hydrogenation of said hydrocarbons, the hydrogen released by the dehydrogenation of part of said hydrocarbons being the sole source of hydrogen for hydrogenating another part of said bydrocarbons, continuing said heating until the reaction is substantially complete and said hydrocarbons have been largely converted into p-cymene and p-menthane, and recovering the pcymene.

C. PALMER.

ROBERT 1.. I-LBBB. 

